Single ground plane junction circulator having dielectric substrate



July 15, 1969 a. HERSHENOV 3,456,213

SINGLE GROUND PLANE JUNCTION CIRCULATOR HAVING DIELECTRIC SUBSTRATE Filed D80. 19, 1966 .mvmior: iamm flzksx/znlov 5r WW4 Q1371;

liter-neg United States Patent US. Cl. 3331.1 3 Claims ABSTRACT OF THE DISCLOSURE A lightweight, compact, microstrip junction circulator includes a plurality of narrow strip conductors radially extending from a conductive disc shaped plate. The narrow conductors are mounted to a slab of dielectric material having an aperture therethrough under the disc plate. A piece of magnetic insulator material of the type exhibiting gyromagnetic effect upon the application thereto of a magnetic field is placed within the aperture and under the disc plate. A planar conductor is affixed to the opposite side of the dielectric slab and magnetic insulator material. Electromagnetic energy propagating between one narrow conductor and the planar conductor is coupled nonreciprocally to the next radially extending narrow conductor and planar conductor in the presence of an applied magnetic field across the magnetic insulator material.

This invention relates to circulators and more particularly to a single ground plane, thin strip transmission line circulator.

The term circulator as used in this disclosure refers to high frequency devices of a type which direct electromagnetic input power therethrough in a nonreciprocal manner and which operate in the manner of a turnstile having ports distributed about its circumference. For example, the case of a three-port circulator, power entering at one port exits at a second port and power entering at the second port exits at the third port, whereby the circu-. lation of power through the circulator is at all times in the same given direction. Circulators are now used extensively to provide radar duplexers, isolators, switching devices and other nonreciprocal transmission line junction devices. The nonreciprocal property of a circulator is determined by a nonreciprocal element disposed at the junction of a plurality of transmission lines which form the ports of the circulator. Generally, the nonreciprocal element comprises a magnetic insulator material such as ferrite or garnet located at the junction of the transmission lines and biased by a magnetic field perpendicular to the plane of circulation. The basic operational principles of a circulator using nonreciprocal elemetns may be found in various texts on the subject such as Microwave Ferrites and Ferrimagnetics by B. Lax and K. J. Button, McGraw-Hill, 1962, pp. 5l7-539, 609-630. The relatively large physical dimensions and weight of the circulator devices previously available has been a problem in the use thereof. Various improvements have been suggested by the demand still exists for an extremely small, lightweight device. With the advent of microelectronics, the consequential need for high frequency circular devices that lend themselves to microwave integrated circuit structure of the type having a single substrate of dielectric material with a ground plane on one broad surface and a narrow strip-like conductor on the opposed broad surface has made the situation more acute.

It is an object of this invention to provide a thin compact lightweight circulator which is readily adaptable for use with microelectronic circuits.

Briefly, there is provided a single ground plane circulator which is formed by coupling a plurality of tranice mission lines to gether at a common point. Each of the transmission lines is made up of a narrow strip conductor closely spaced from a wide planar conductor by a material having a relatively high dielectric constant. The width of the planar conductor is made substantially greater than that of thet narrow conductor so that electromagnetic waves approximating the TEM mode can be propagated therebetween. The spacing between the couductors of a transmission line is made sufficiently small and the dielectric constant of the spacer material is made sufiiciently large such that the electromagnetic fields are distributed mainly between the opposed surfaces of the conductors of a line and insignificant radiation occurs outside the lines. Magnetic insulator material is placed between the junction of the narrow conductors of the respective lines and the wider or planar conductors of the respective lines. In practice, the wider or planar conductors of the respective lines can be formed as a unified, single planar conductor or ground plane for the circulator. The magnetic insulator material when properly biased by a magnetic field in a direction parallel to the electric field of electromagnetic waves in the TEM mode propagated along one of the lines serves to couple the wave energy only to one other of the lines in a nonreciprocal manner. A small, lightweight, single ground plane circulator is provided which is particularly suited for use with integrated and other microelectronic circuits.

The above mentioned and other features and objects of this invention will become apparent by reference to the following description taken in conjunction with the accompanying drawings wherein:

FIGURE 1 is a cross-sectional view of a strip transmission lines;

FIGURE 2 is a plan view of a circulator constructed in accordance with an embodiment of the invention;

FIGURE 3 is a cross-sectional view taken along the line 33 of FIGURE 2;

FIGURE 4 is a cross-sectional view of another embodiment of the present invention.

Referring to FIG. 1 of the drawing, there is illustrated a strip transmission line. This line propagates in a mode approximating a TEM mode and comprises a narrow line conductor 10 and a single ground planar conductor 11 with a layer 13 of dielectric material spaced therebetween. The conductive material to form conductors 10, 11 may be applied as a thin layer to the dielectric material 13. The conductive material may be chemically deposited, sprayed through a stencil or dusted onto selected surfaces of the dielectric 13 according to the known printed circuit techniques. The ground conductor 11 should preferably be from two or three times the width of the narrow conductor 10, although wider dimensions still give lower loss. The thickness of the transmission line and the dielectric constant used should be such as to prevent radiation from the line.

FIGURE 2 shows a plan view of a Y-junction 3-port circulator 20 in accordance with an embodiment of this invention utilizing the form of transmission line described above in connection with FIGURE 1. While a particular type of circulator, namely, a Y-type circulator, will be described, it is to be understood that the teachings of the invention may be employed to provide other known types of high frequency devices which operate to direct electromagnetic wave energy in a nonreciprocal manner. The circulator 20 includes a coaxial coupler at a first port 21, at a second port 22 and at a third port 23. Narrow line conductors 25, 26 and 27 each similar to the line conductor 10 described above in FIGURE 1 extend radially from a common point where there is provided a thin copper disc 29. The narrow conductors 25, 26 and 27 are coupled to the respective center conductors of the coaxial couplers at ports 21, 22 and 23. The narrow conductors 25, 26, 27 extend radially 120 degrees apart from disc 29 to provide a symmetrical Y-junction three-port circulator. The line conductors 25, 26 and 27 can be thin copper strips and are fixed to the top surface of a substrate 30. The copper disc 29 to which the narrow conductors 25, 26 and 27 are connected is centered and also fixed to the same surface of the substrate 30. A thin copper ground plane 33 (not shown in FIG. 2) is fixed on the bottom or opposite surface of the substrate 30 with respect to the narrow conductors 25, 26, 27. Various available techniques for forming a conductor on the substrate 30 to produce the narrow line conductors, the disc, and the ground plane conductor, for example, glueing or evaporation of the conductors, may be used.

The conventional strip transmission line circulator now in use includes a plurality of narrow center conductors extending radially from a common point and a ground plane on either side of the center conductors so that the discontinuities of the circulator strip transmission line may be geometrically belanced with respect to the upper and lower sections of the lines to suppress radiation.

In accordance with a circulator of this invention, the spacing between the narrow strip conductors 25, 26, 27, disc 29 and the single planar conductor 33 is made so small (less than half a wavelength of a TEM electromagnetic wave propagated in the dielectric medium) that little radiation exists outside the lines. Also, by making the spacing small and using a relatively high dielectric material for the substrate 30 (dielectric constant of 9.4, for example) between conductors 25, 26, 27, disc 29 and the conductor 33, the electromagnetic fields are distributed mainly between the opposed conductive surfaces (between disc 29 and the opposed surface of conductor 33 and between narrow conductors 25, 26 and 27 and the opposed surface of conductor 33). The possibility of radiation due to discontinuities is thereby reduced. Also, by making the dielectric constant relatively high, the overall size of the circulator 20 is small. Since the open sides of the circulator are thin, there is also a poor output impedance match to free space at the open sides.

To complete the construction of a nonreciprocal junction circulator as shown in FIG. 1, a magnetic insulator is needed and provision should be made for the application of a magnetic field in a direction parallel to the electric field of an electromagnetic wave in the TEM mode conducted by the lines. The magnetic insulator material may be for example garnets, ferrites, and other magnetic materials. The strength of the DC. magnetic field and the direction in which the field is applied is arranged so that circulation of the electromagnetic wave energy in a desired direction is achieved for the frequency range of interest.

FIGURE 3 shows a cross-sectional view of the embodiment of the invention shown in FIG. 2, wherein the narrow conductors 25, 26 and 27 are positioned on the top surface of a dielectric substrate 30. A disc of magnetic insulator material 36 is placed in a hole cut in the center of the dielectric substrate 30 shown in FIGURE 3. The disc 36, for example, may have a dielectric constant of approximately 16 and the dielectric substrate 30 may have a dielectric constant of approximately 9.4. This duodielectric interface acts as the walls of a cavity to confine the electromagnetic energy in the TEM mode in the neighborhood of the copper disc 29 and the disc 36 of magnetic insulator material. The copper disc 29 is fixed above the disc of magnetic insulator material 36 by evaporation or other known techniques and connects with the narrow conductors 25, 26 and 27. For purposes of testing, a brass holder 38 having a hole cut in the center is shown placed below the ground plane 33. The ground plane 33, as above, is fixed by evaporation of other known techniques to the opposite side of the substrate 30 with respect to the copper disc 29. A small permanent magnet 39 may be placed inside the hole of the holder 38 just below the disc of magnetic insulator material 36 as shown.

In the operation of the embodiment shown in FIG- URE 3, coaxial cables are connected to ports 21, 22 and 23. The magnet 39 is arranged so that a magnetic field below resonance is developed in the direction of arrow 40. When the magnetic insulator material 36 is biased with the external D.C. magnetic field provided by magnet 39, a nonreciprocal condition exists whereby electromagnetic signal energy approximating the TEM mode entering the port 21 exits only at port 22. In a similar manner signal energy entering at port 22 exits at port 23, and signal energy entering at port 23 exits at port 21. The direction of circulation can be reversed by reversing the direction of the applied magnetic field supplied by the permanent magnet 39. Greater than 20 db of isolation was provided when operating a device similar to that described above for signal energy from 8.3 to 9.45 gHz. (gigohertz) with a total insertion loss of less than 0.5 db over the entire band. The device tested comprised the following components and values:

Substrate 30-0.023-inch thick, Alsimag 772 (made by American Lava Corporation, Chattanooga, Tenn). Narrow conductors 25, 26 and 27-0.132-inch long and 0.03-inch wide copper.

Disc 290.22-inch diameter copper.

Magnetic insulator 360.22-inch diameter and 0.023-inch thick, garnet G113 (made by Trans-Tech Inc., Gaithersburg, Md.).

Magnet 390.l5-inch long and 0.3-inch diameter Indox 6 (made by Indiana Steel Products Division, Valparaiso, Ind.).

The magnet 39 was placed 0.024 inch from the magnet insulator 36. The copper conductor 25, 26, 27, 29 and 33 where about 0.0005-inch thick. The DC. magnetic field provided by the magnet 39 was approximately 792 oersteds.

It is possible to place a permanent magnet or an electromagnetic at the top and bottom of the magnetic insulator material 36 for biasing the magnetic material. Any of the known methods for providing this D.C. magnetic field bias such as latching may be used in accordance with the teachings of this invention. It is possible to operate at a different range of frequencies and in different directions of circulation by operating the circulator above resonance.

FIGURE 4 shows a cross sectional view of a circulator in accordance with another embodiment of the present invention. This embodiment shows the narrow line conductors 26 and 27 fixed to the top surface of a magnetic insulator material 30. In the example shown in FIGURE 4 the conductors are evaporated onto a garnet substrate 30. The narrow conductors are connected to a conductive disc 29 which is evaporated and centered on the same surface of the garnet substrate 30 as are the narrow line conductors 25, 26 and 27. On the bottom or opposite side of the magnetic insulator material substrate 30 is evaporated a ground plane conductor 33. In this manner a single slab of magnetic insulator material is spaced between the conductive materials providing a simple construction and one which is readily adaptable for use in microcircuits. In this embodiment the copper disc 29 is placed so that it tends to localize an input electromagnetic RF field in the region of the copper disc 29. This small region behaves like a cavity much in the same manner as does the garnet disc 36 when it is embedded in a dielectric medium 30' as described in connection with FIGURE 3. In the operation of the embodiment shown in FIGURE 4, coaxial cables are coupled to ports 21, 22 and 23. The magnetic insulator material substrate 30 is biased with an external magnetic field in a direction as shown by arrow 41 in the small region between the copper disc 29 and ground plane 33. A nonreciprocal action takes place whereby electromagnetic signal energy entering at port 22 exits at port 23, and so on. The direction of circulation may be reversed by reversing the direction of the magnetic field. Greater than 20 db of isolation was provided when operating a device similar to that described above in connection with FIG. 4 for signal energy from 7.9 to 9.05 gHz. with a total insertion loss of less than 0.5 db over the entire band. The device constructed and tested had the following components and values:

Magnetic insulator material substrate 30--0.023-inch thick garnet 61200 (made by Trans Tech Inc.).

Narrow line conductors 25, 26 and 270.127-inch long and 0.025-inch wide copper.

Disc 290.23-inch diameter copper.

Magnet 390.3-inch diameter and 0.15-inch long Indox 6.

A permanent magnet was placed 0.005 inch from sub strate 30 and provided a DC. magnetic field which at the top center of the magnet face is approximately 1500 oersteds. The conductors 25, 26, 27, 29 and 33 were 0.0005-inch thick copper evaporated to the substrate 30.

It is again possible to place a permanent magnet or an electromagnet above or below the substrate 30 for biasing the magnetic material. Any of the known methods for providing this D.C. magnetic field such as latching may be used in accordance with the teachings of this invention.

The circulator 20 shown in FIGURES 2, 3 and 4 is illustrated and described only for illustrative purposes. It is possible using the above techniques described in connection with circulation 20 to construct other types of microwave devices that direct electromagnetic input power in the circulation manner described above.

What is claimed is:

1. A small compact lightweight microwave circulator which is readily adaptable for use with microwave integrated circuit structures of the type having a single substrate of dielectric material with a ground plane on one broad surface and a narrow-strip-like conductor on the opposed broad surface, said circular comprising:

only a single substantially flat substrate of dielectric material,

a plurality of narrow strip-like conductors directly connected together at a common conductive region and fixed to one broad surface of said second-mentioned substrate with said last-mentioned conductors ex tending radially on said one broad surface of said second-mentioned substrate from said common conductive region,

a single ground planar conductor which is the only ground conductor for said circulator fixed to the opposite surface from said one surface of said second-mentioned substrate, said single planar conductor forming with said strip-like conductors a plurality of separate transmission lines junctured at said common conductive region with said secondmentioned substrate occupying the entire area between all of said strip-like conductors of said circulator including that portion at said common conductive region and said planar conductor in said circulator,

said second-mentioned substrate in the area thereof disposed between said common conductive region and said planar conductor being made entirely of magnetic insulator material of the type exhibiting a gyromagnetic efiect in response to a magnetic field applied thereto, the material of said second-mentioned substrate having a dielectric constant of at least about nine to cause with the construction of said circulation at most only an insignificant loss of energy through radiation external to said circulator.

2. A circulator as claimed in claim 1 and wherein said second-mentioned substrate is made entirely of said magnetic insulator material.

3. A small compact lightweight microwave circulator which is readily adaptable for use with microwave integrated circuits of the type characterized by a single substrate of dielectric material with a ground plane on one broad surface and a narrow strip-like conductor on the opposed broad surface, said circulator comprising:

only a single substantially flat substrate of dielectric material,

a plurality of narrow strip-like conductors directly connected together at a common conductive region and fixed to one broad surface of said second-mentioned substrate with said last-mentioned conductors extending radially on said one broad surface of said second-mentioned substrate from said common conductive region,

a single ground planar conductor which is the only ground conductor for said circular fixed to the opposite broad surface from said one surface of said second-mentioned substrate, said planar conductor forming with said strip-like conductors a plurality of separate transmission lines junctured at said common conductive region with said second-mentioned substrate occupying the entire area between all of said strip-like conductors of said circular including that portion at said common conductive region and said planar conductor in said circulator, and

said second-mentioned substrate being made entirely of magnetic insulator material of the type exhibiting a gyromagnetic effect in response to a magnetic field applied thereto and having a dielectric constant sufficient to cause with the construction of said circulator only an insignificant loss of energy through radiation external to said circulator.

References Cited UNITED STATES PATENTS 3,295,074 12/1966 Carr 3331.1

3,339,158 8/1967 Passaro 333-1.1

3,063,024 11/1962 Davis 3331.1

3,257,629 6/1966 Kornreich 333--31 3,334,318 8/1967 Nakahara et a1. 3331.1

OTHER REFERENCES Harvey: Parallel-Plate Transmission Systems for Microwave Frequencies, the IEE, March 1959, pp. 129- 133 relied on.

HERMAN KARL SAALBACH, Primary Examiner P. L. GENSLER, Assistant Examiner U.S. Cl. X.R. 333-84 mg UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3455 211 Dated July 15 1060 Inventr(g) Bernard Hershenov It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

W01. 1, line 52, correct "elemetns" to read elements Co] 1 line 59, correct "by" to read but Col. 1, line 61 correct "circular" to read circulator Col 2, line 1, correct to gether" to read together Cc 2, line 6, correct "thet" to read the Col. 2, line 33, correct "lines" 'to read line Col. 3, line 21, correct "belanced" to read balanced Co] 3, line 72 after "evaporation" correct "of" to read or Col. 4 line 17, correct "(gigohertz)" to read (g igahertz) Col 4, line 73, after "at port" insert 21 exits .at port 22. Signal energy entering at port C01. 5, line 26, correct "circulation" to read circulator Col. 5, line 35, correct "circular" to read circulator Col. 6, line 4, correct "circulation" to read circulator Col 6 line 33, correct circular" to read circulator SIGNED KND SEALED JUN 1 6 1970 sEm mt:

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mm E. a: Attesung Officer Gomissioner of Pedant 

